Fine structure and selection rules for excitonic transitions in silicon nanostructures

The excitonic fine structure, including splitting due to direct and exchange interactions, has experimentally been resolved from silicon nanocrystals and from silicon nanorods. We have found the hierarchy of levels for silicon nanorods to be different from that of silicon nanocrystals with the slower semidark state located above the faster semibright state. The results are analyzed in terms of spin and orbital selection rules indicating that the dimensionality of the exciton determines the relative contribution of the direct Coulomb and the exchange interactions in these nanostructures.